WASHINGTON (AP) _ The Forest Service sought to obtain 100 tactical bombers from the Air Force in 1991, saying it wanted to convert the aircraft to fight forest fires, government documents indicate.

The Pentagon concluded the request for surplus A-10 ''warthogs'' was too steep and there would be technical difficulties in attaching 1,500-gallon tanks to the bombers for use in firefighting, the documents show.

A congressional subcommittee chaired by Rep. Charlie Rose, D.-N.C., is investigating allegations the Forest Service may have been trying to obtain military aircraft that could be used in covert CIA operations.

Those allegations have been fueled by revelations that two C-130 cargo planes the Forest Service had obtained from the military for forest fighting had turned up unexplained in Kuwait after the Persian Gulf War.

Forest Service Chief Dale Robertson has acknowledged mistakes with the C- 130s. But he has played down the agency's interest in the A-10s, the Air Force's primary tank-attack plane.

Robertson told Congress last month the interest in the A-10s was fleeting, amounting to brief discussions with the Pentagon and one contact with a private contractor. No purchases were made, he said.

''Nothing ever happened to that,'' Robertson told the House Agriculture subcommittee chaired by Rose.

But an April 22, 1992, memo from the then-assistant director of the Forest Service's aviation program indicates a formal request was made to the Air Force for the planes in 1991.

''FS (Forest Service) request to the AF (Air Force) was for 100 A-10s,'' Fred Fuchs wrote in an electronic message to Richard Denker, the Forest Service's contracting officer in Boise, Idaho.

''AF has indicated that 100 was a reasonable number,'' according to the the Fuchs memo obtained by The Associated Press.

Fuchs wrote that ''we lost some ground by messing around and not starting the project last year,'' so that the request was trimmed back to just two planes to develop prototypes in 1992.

''Current request if for 2 A-10s and the original request for 100 is still at the AF. Recent discussions I had told that they have about 20 or 30 they could transfer,'' he wrote.

Associate Deputy Forest Service Chief Charles R. Hartgraves said Friday he did not believe Fuchs' memo accurately portrayed the agency's interest in the A-10s.

He said the agency in August 1990 considered seeking 100 A-10s, but ''to my knowledge, we have never asked the Air Force for 100. The most we ever asked to set aside was 10.''

''I think the electronic message is Fred Fuchs' version of it,'' Hartgraves said. ''There is no indication the Air Force agreed. It might have been wishful thinking on his part.''

Fuchs, who longer holds that job, could not be located for comment.

A spokesman for the Pentagon said no one was available to comment.

The Forest Service last month released a Defense Department study and a letter from Rep. Bob Smith, R-Ore., indicating the Pentagon was considering the Forest Service request and had done a feasibility study on converting A- 10s for firefighting.

''Revised DOD force structure requirements and potential foreign military sales may preclude release of large numbers of aircraft requested by the Forest Service. Realistically, a smaller number of A-10s may become available, perhaps as many as 20 to 30,'' the DOD report said.

The Pentagon said it determined there would be significant problems in attaching a 1,500-gallon tank to the bombers to drop water on forest fires because of the aerodynamic effects of the external tank.

The DOD study also suggests the Forest Service was interested in equipping the A-10s with infrared radar to enable the planes to drop retardants on fires at night.

James Ebbitt, the Agriculture Department's assistant inspector general, has told Congress there was a consensus in the aviation industry that A-10s likely could not be used effectively to fight fires.

The inspector general said in a report last fall that taxpayers lost $67 million under Forest Service's aviation program because the agency had traded away C-130s it got from the military to preferred contractors at below-market prices.

Assistant Agriculture Secretary Jim Lyons has confirmed the Justice Department is investigating possible criminal wrongdoing related to those deals.

Rose, whose committee is also investigating the Forest Service, said he suspects the planes really were being sought to assist the CIA.

The Forest Service has halted transfers of such planes and acknowledged mistakes had been made. But it has denied any connection to the CIA or covert uses for the planes.